Segmented ball/roller guide for a linear motion bearing

ABSTRACT

A guide ( 10 ) associated with a linear motion and screw system is configured to at least partially surround one of a plurality of rolling elements ( 20 ) so as to prevent ball-to-ball contact between the one rolling element and adjacent rolling elements during displacement of the rolling element along a circulation ball track.

CROSS-REFERENCE TO RELATED APLICATION

This application is based on U.S. Provisional Application No. 60/360,155filed on Feb. 27, 2002 and fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to anti-friction linear motionbearing assemblies. More particularly, the present invention is directedto a segmented ball/roller guide assembly utilized to eliminatevibrations caused by ball-to-ball contact in linear motion bearings.

2. Description of the Related Art

Linear bearings or ball screws are well known for their significantreduction in dynamic and static friction versus plain bearings or leadscrews under load. There are different types of linear bearings and ballscrews offered on the market today. However, they share a common focusto control ball recirculation properly to provide smooth linear orrotary motion.

Typical linear rolling bearing assemblies include a series of rollingelements moving about a circulation path which circulation path isformed in the periphery of a track member and a surrounding andenclosing bearing cover confining the rolling elements in theirrecirculation path. In order to achieve an accurate linear motion, theaxis of the bearing assembly must be precisely aligned with the desireddirection of motion along the supported structure. In addition thisprecise alignment also minimizes skewing forces acting on the bearingassembly, which skewing forces tend to reduce the load/life performanceof the bearing assembly.

Installation of such bearing assemblies on a supporting structure (i.e.,shaft, splined shaft, guideway or rail) typically involves precisionmachining of locating surfaces in order to properly align the bearingassembly on the supporting structure. Such bearing assemblies aretypically installed in sets, each comprised of a number of variouslyfacing bearings such as to engage a series of surfaces on the supportingstructure (i.e., such as above and below a supporting surface and/oralong a lateral edge of a supporting surface). In such instances it isusual to provide a bearing adjustment for enabling precision adjustmentof the bearing assembly on the supported structure and also forestablishing a proper bearing pre-load by adjusting an opposing bearingassembly for reasons well known to those skilled in the art. In suchinstallations, considerable precision machining of the supportedstructure is necessitated which is difficult and expensive to accomplishon the supporting structures.

Many of the disadvantages discussed were overcome in a linear motionbearing structure disclosed, among others, in U.S. Pat. Nos. 5,346,313;5,558,442; 5,613,780 issued to Alison Ng and commonly owned by ThomsonIndustries, Inc., and fully incorporated in this application byreference. The above-identified patents, and particularly the U.S. Pat.No. 5,613,780, disclose a linear motion bearing assembly comprising aplurality of ball retainer segments including at least one ball trackhaving a load bearing portion, a return portion and a turnaroundportion. A plurality of individual balls is then disposed in the balltrack to enable the linear bearing to provide low friction motion.

Such low friction is particularly advantageous in structures related tobiased linear motion bearing assemblies of the type, which support acarriage or a pillow block for linear movement along an elongatedsplined shaft. These bearing assemblies can either be of the open typeor the closed type.

Typically, in the linear bearing assemblies, as disclosed in theabove-identified patents, the ball-to-ball contact in the ball trackgenerates adverse conditions when the bearing is in operation. Theball-to-ball contact generates mechanical and/or acoustic vibrations.Radial bearing industries created ball cage technology to eliminatevibration due to ball-to-ball contact. However, recent developments inlinear bearing technologies are working toward elimination of theball-to-ball contact itself.

One such development is a rolling element chain, also known as a ballchain. Rolling element chains are designed to contain a row of rollingelements, i.e., a ball, as one subassembly with separators between therolling elements to avoid ball-to-ball contact. An example of one suchrolling element chain is disclosed in U.S. Pat. No. 5,947,605 to Shirai.The rolling element chain is made usually from very flexible material toallow ball recirculation. Additionally, careful material selectionimproves the vibration dampening characteristics of the ball chain.

As much as it is beneficial to the reduction of noise or vibration, therolling element chain also has its drawbacks. The rolling element chaindoes not provide designers with much freedom in designing ball trackgeometry. Due to the single chain mechanism, rolling elements mustfollow a track geometry that is normal or nearly normal to the directionof an applied load on the ball track. This restricts the location of thereturn track geometry for the ball track and often results in anunwanted outside bearing envelope dimension increase or modification dueto the location of return geometry for the rolling elements. If thebearing requires a very strict return geometry away from the directionnormal to the applied load on the ball track, the rolling element chainmust be made from very flexible material to allow more twist. However,this is a very undesirable design due to long term effects on thematerial when it is twisted constantly.

Another development towards the elimination of ball-to-ball contact inlinear motion and ball screw systems is a ball spacer. Ball spacers areindividual pieces of a material, such as a resin or polymer, whichseparate rolling elements in a bearing or ball screw. Ball spacers allowelimination of ball-to-ball contact without the restrictions provided bythe rolling element chain. Individual ball spacers do not haveconnections between them like the rolling element chain and allowdesigners to implement ball-to-ball separators without major change inball track geometry.

Although ball spacers allow more freedom in designing ball returngeometry, they do have disadvantages. Due to the use of individualspacers, designers must ensure the spacers will not fall out of itsposition during operation. If the spacers are dropped out of itsposition between the balls to the bottom or sides of the ball track,they will create severe impediments to linear motion. This could resultin a catastrophic failure on the bearings.

U.S. Pat. No. 6,352,367 illustrates the above-discussed drawback bydisclosing a spacer located between adjacent rolling elements andconfigured so that if the distance between the balls exceeds the outerdimension of the spacer, it can be easily displaced off a ball track,which leads to the consequences discussed above.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide anew ball-to-ball separator technology, which will eliminate thedisadvantages of the prior art rolling element chains and ball spacers.

It is another object of the present invention to provide a segmentedball/roller guide for eliminating ball-to-ball contact in linear motionbearings.

It is a further object of the present invention to provide a segmentedball/roller guide for reducing mechanical and/or acoustic vibrations inlinear motion bearings.

It is yet another object of the present invention to provide a segmentedball/roller guide which allows greater flexibility in designing returntrack geometry.

The inventive ball/roller guide assembly has a guide configured tosupport and guide at least one rolling element so that, even if adistance between adjacent rolling elements displaceable along a balltrack becomes large enough for the guide to drop off the track, itremains on the track. Accordingly, since the guide is prevented fromunacceptable displacement that, otherwise, could result in impedimentsto the linear motion, it maintains the desired alignment betweenadjacent rolling elements along the ball track eliminating.

The segmented ball/roller guide of the present invention includes afirst spacer member, a second spacer member and at least one connectionmember for connecting and supporting the first and second spacer at anequal diametrical distance around a ball bearing. The first and secondspacer members are formed generally in a disc-like shape and may beformed with at least one concave surface so when assembled the ballbearing will be rotatably held within the segmented ball/roller guide.Preferably, the guide is dimensioned to maintain a substantiallycontinuous sliding contact with the thus supported ball baring. In use,the ball bearing will circulate on a ball track of a linear motionbearing with the spacers preventing ball-to-ball contact. Since eachsegmented ball/roller guide includes two spacer members, only onesegmented ball/roller guide is required for every other ball of aplurality of balls placed on the ball track of a linear motion bearing.Additionally, the connection member acts as a guide for the ball whencirculating around the ball track.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become more apparent in light of the following detaileddescription of exemplary embodiments thereof taken in conjunction withthe attached drawings in which:

FIG. 1 is a perspective view of a first embodiment of a segmented ballguide assembly in accordance with the present invention;

FIG. 2 is a plan front view of the first embodiment of a segmented ballguide assembly in accordance with the present invention;

FIG. 3 is a perspective view of the segmented ball guide of FIG. 1 withthe ball removed;

FIG. 4 is a perspective view of the support/guide structure of thesegmental ball guide sown in FIG. 1 in accordance with the presentinvention;

FIG. 4A is a cross-sectional view taken along lines I-I in FIG. 4;

FIG. 5 is a perspective view of another embodiment of a support/guidestructure of a segmented ball guide in accordance with the presentinvention;

FIG. 6 is a perspective view of still another embodiment of asupport/guide structure of a segmented ball guide in accordance with thepresent invention;

FIG. 7 illustrates a plurality of segmented ball guide assemblieslocated in a load bearing portion of a ball track of a linear bearingassembly;

FIG. 8 is an enlarged view of FIG. 7; and

FIG. 9 is a perspective view of a still another embodiment of asegmented ball guide in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the invention in unnecessarydetail. It is provided that identical elements are structurally andfunctionally equivalent throughout the drawings.

Referring to the FIGS. 1-8, a segmented ball/roller guide in accordancewith the present invention is identified generally by the referencenumeral 10.

FIGS. 1-5 illustrates a segmented ball/roller guide assembly 100 with aball bearing contained therein. The segmented ball/roller guide 10 ofthe present invention includes at least one first spacer member 12.While the first spacer member 12 can completely or partially surround arolling element, such as a ball bearing 20, as will be discussedhereinbelow, many of the inventive modifications of the support/guide 10include a second spacer 14. The spacers 12 and 14 are spaced from oneanother along a travel direction and function as a guard preventingcontact between adjacent ball bearings 20 travelling along a track. Thedistance between the spacers 12 and 14 may be selected so that it is atleast slightly greater than the outer diameter of the ball bearing 20.As a result, at least the trailing portion of the guide 10 maintains asubstantially continuous sliding contact with the ball bearing 20without detrimentally affecting the rotation of the ball bearing.Preferably, as a result of the geometry of the spacers 12, 14 and theball bearing 20, the former are spaced at a uniform radial distancearound the ball bearing 20 and are juxtaposed with its leading 23 andtrailing 21 segments or regions, respectively. To maintain such auniform distance, the inventive assembly includes at least one firstconnection member 16 (FIG. 5), but, preferably, two connection members16 and 18, as better illustrated in FIGS. 1-4.

To reliably guide the ball bearing 20, the first and second spacermembers 12, 14 may be formed with seats each having a respective concavesurface 22, 24 (see FIG. 3) extending complementary to the regions 21,23 of the ball bearings 20. Accordingly, when assembled, the ballbearings 20 will be rotatably held within the segmented guide 10 and,even if a distance between adjacent ball bearings 200-206 (FIG. 8) isunacceptably increased, the guide 10 remains in sliding contact with theguided ball baring. In practical terms, the guide 10 cannot be displacedfrom its position between adjacent ball bearings running along acirculation passage of a ball track formed in a bearing carriageregardless of their relative position along the ball track. Preferably,the spacer members 12, 14 will have concave surfaces formed on bothsides 24, 26 one to retain the ball 20 and one for contact with anadjacent ball when in motion, the operation of which will be describedbelow. Alternatively, however, the inner surfaces 22, 24 can be flat oreven convex to still provide contact with the leading 23 and trailing 21regions of the ball bearing 20.

FIGS. 4 through 6 illustrate various embodiments of the segmentedball/roller guide. Fundamentally, the variations in the differentembodiments are in the number and structure of the connection members.As shown in FIG. 5, the ball/roller guide 10 includes only oneconnection member 16, whereas the embodiment shown in FIG. 6, has one ofthe connection members recessed. The geometry and particular structureof the connection members 16, 18 depend the particular design of theball track. Advantageously, bottoms 17 and 19 of the connection elements16, 18 are narrowed to have an arcuate or substantially conical shape(FIG. 4A), which will reduce a contact area and, consequently,frictional forces between the connection elements and side surfaces ofthe ball track. Operationally, the embodiments shown in FIGS. 4 through6 are functionally similar. The spacers 12, 14 as well as connectionelements 16 and 18 can be detachably coupled to one another by variousfasteners. In addition, the guide can be configured to have all of thecomponents machined with surfaces extending complementary to andmatching one another during the assembly of the guide 10. For example,the spacers 12, 14 each can have recesses receiving complementary formedprojections of the connection elements 16, 18. Alternatively, thecomponents of the ball/roller guide can be made integrally or unitarilyfrom a variety of materials including engineering polymers andthermoplastics characterized by a low-friction coefficient.

In use, the segmented ball/roller guide will circulate on a ball trackof a linear motion bearing with the spacer members preventingball-to-ball contact. FIGS. 7 and 8 show a ball retainer segment orbearing carriage 72 of a linear bearing assembly 70. The ball retainersegment 72 includes a ball track 74 having a load bearing portion 76, areturn portion 78 and a turnaround portion 80. Since each segmentedball/roller guide 10 includes two spacer members 12 and 14, only onesegmented ball/roller guide 10 is required for every other ball of aplurality of balls placed on the ball track 74 of linear bearing 70.Spacer members 12 and 14 will retain a first ball 200 and a second ball202 will circulate in the outer concave surface 26 of spacer member 14and an outer concave surface (not shown) of spacer member 12 of the nextadjacent guide 10. As the balls 200, 202, 204, 206 circulate to providelinear motion the spacer member 12, 14 will eliminate ball-to-ballcontact. Additionally, the connection member or members 16, 18 act as aguide for the balls 20 when circulating around the ball track 74 whilepreventing the displacement of the balls off the track.

FIG. 9 illustrates a fifth embodiment of the segmented ball guide. Asshown in FIG. 9, the guide 90 is formed as an annular member having aninner surface 92, an outer surface 94, a top surface 96 and a bottomsurface 98. The guide is preferably formed with flat surfaces. As amodification to the annular member, the inner surface 92 and outersurface 94 may be formed in a concave shape to minimize the spacingbetween balls 20. As with the other embodiments described above, theannular member 90 will act as a guide for the balls when circulatingaround the ball track.

The present invention allows the benefits of both the rolling elementchain and ball spacers to be used without the associated disadvantages.The segmented ball/roller guide of the present invention acts in verymuch the same manner as the rolling element chain without thedisadvantage of limited twist. By not having the individual segmentedball guide assemblies connected to each other, an infinite amount oftwist between the ball guides is possible resulting in a great amount offlexibility in designing the return track geometry.

Furthermore, the segmented ball/roller guide is not in danger of fallingout of position when the gap between rolling elements, i.e. bearingballs, increases over time as occurs with ball spacers. This is achievedby the connection member or members 16, 18 between the ball spacermembers. This allows designers of linear bearings to ease the tolerancerequirements in ball track geometry. This also allows designers freedomto choose either hard or soft material for the segmented ball/rollerguide since changes in the gap distance between balls will not result incatastrophic failure.

While the present invention has been described in detail with referenceto the preferred embodiments, they represent mere exemplaryapplications. For example, the ball bearing 20 can be incorporated inradial bearings. Outer surface 85 (FIG. 9) of at least one of thespacers 12, 14 can be recessed along the trailing or leading regions 23,21 of the rolling element 20 so that a shape and size of recess allowsan adjacent ball bearing to be guided and supported. Thus, it is to beclearly understood that many variations can be made by anyone havingordinary skill in the art while staying within the spirit and scope ofthe present invention.

1. A guide assembly for at least one rolling element displaceable alonga path, comprising a guide configured to guide the at least one rollingelement along the path while maintaining a substantially continuoussliding contact therewith along the path.
 2. The guide assembly of claim1, wherein the guide includes at least one spacer extending betweendiametrically opposite leading and trailing regions of the at least onerolling element.
 3. The guide assembly of claim 2, wherein the at leastone spacer is endless.
 4. The guide assembly of claim 2, wherein the atleast one spacer is discontinuous along one of the leading and trailingregions of the at least one rolling element.
 5. The guide assembly ofclaim 2, wherein the at least one spacer has opposite inner and outersides extending either parallel to one another or converging toward thebottom so as to reduce a contact surface of the bottom.
 6. The guideassembly of claim 5, wherein the bottom has an arcuate or substantiallyconical.
 7. The guide assembly of claim 5, wherein the inner side of theat least one spacer has at least one portion juxtaposed with arespective one of the leading and trailing regions of the rollingelement and being curved to maintain the substantially continuouscontact with the respective one of the leading and trailing regions. 8.The guide assembly of claim 7, wherein the curved portion of the spacerhas a surface extending complementary to the respective one of theleading and trailing regions of the at least one rolling element.
 9. Theguide assembly of claim 5, wherein the outer side of the at least onespacer has a region provided with a curved surface configured toslidingly support a second rolling element located immediately upstreamor downstream from the at least one rolling element.
 10. The guideassembly of claim 2, wherein the guide further comprises: a secondspacer juxtaposed with a respective one of the leading and trailingregions of the at least one rolling element, the second spacer beingconfigured to maintain the substantially continuous contact with the atleast one rolling element, and at least one connector extending betweenand coupling the at least one and second spacers to ensure thesubstantially continuous contact between the at least one rollingelement and the second spacer during the displacement of the at leastone rolling element along the path.
 11. The guide assembly of claim 10,wherein the guide further comprising a second connector spaced from theat least one connector and extending between the at least one and secondspacers, so as the at least one rolling element is surrounded by theguide.
 12. The guide assembly of claim 11, wherein one of the at leastone and second connectors is discontinuous.
 13. The guide assembly ofclaim 11, wherein the at least one and second connectors and the atleast one and second spacers are detachably assembled or unitarilyformed.
 14. The guide assembly of claim 11, wherein the guide is madefrom materials selected from the group consisting of polymers,thermoplastics and a combination of polymers and thermoplastics andcharacterized by a low-friction coefficient.
 15. A linear motion andball screw system comprising: an endless circulation passage; aplurality of rolling elements displaceable in the endless circulationpassage along a travel direction; and at least one guide receiving theplurality of rolling elements and configured to prevent ball-to-ballcontact between the one rolling element and upstream and downstreamrolling elements which are located adjacent to the one rolling element.16. The linear motion and ball screw system of claim 15, wherein the atleast one guide comprises: a leading spacer located between the at leastone rolling element and the downstream rolling element and spanning thecirculation passage; a trailing spacer located between the at least onerolling element and the upstream rolling element and spanning thecirculation passage; and at least one connector extending between andconnected to the leading and trailing spacers and extending laterallybeyond the circulation passage to at least partially enclose the atleast one rolling element.
 17. The linear motion and ball screw systemof claim 16, further comprising a second connector spaced diametricallyfrom the at least one connector and extending between the leading andtrailing spacers and laterally beyond the circulation passage.
 18. Thelinear motion and ball screw system of claim 17, wherein at least one ofthe one and second connectors is discontinuous to reduce frictionbetween the connectors and a surface adjacent to the circulationpassage.
 19. The linear motion and ball screw system of claim 16,wherein at least one of the leading and trailing spacers has oppositeinner and outer surfaces curved inwards toward one another to form afirst seat for the at least one rolling element and a respective one ofthe upstream and downstream rolling elements.
 20. The linear motion andball screw system of claim 16, wherein the guide is configured to havethe leading and trailing spacers spaced uniformly from a rolling axis ofthe at least one rolling element.
 21. The linear motion and ball screwsystem of claim 16, wherein the at least one rolling element and atleast the trailing spacers are in substantially continuous contactduring displacement of the at least one rolling element long thecirculation passage.
 22. The linear motion and ball screw system ofclaim 17, wherein the leading and trailing spacers and the one andsecond connectors are detachably connected to one another or fixed toone another.
 23. A linear motion bearing comprising: a bearing carriageprovided with at least one endless circulation passage; a series ofindividual bearing balls movable along the circulation passage; and aplurality of guides slidable along the circulation ball passage andarranged to have every other bearing ball guidingly supported in arespective guide and to prevent adjacent bearing balls from ball-to-ballcontact during displacement of the bearing balls.
 24. The linear motionbearing of claim 23, wherein the plurality of guides each comprises: aleading spacer spanning the circulation passage; a trailing spacerlocated upstream from the leading spacer and spanning the circulationpassage; and at least one connector extending between and connected tothe leading and trailing spacers and extending laterally beyond thecirculation passage, whereas, as the series of bearing balls moves alongthe circulation passage, the guides and the bearing balls are insubstantially continuous contact.
 25. The linear motion bearing of claim24, further comprising a second connector spaced diametrically from theat least one connector.